1. Field of the Invention
The present invention relates to a material for probe pins to be incorporated in a probe card to inspect the electrical properties of an integrated circuit formed on a semiconductor wafer.
2. Description of the Related Art
A probe card in which multiple probe pins are arrayed is used in performing the inspection of the electrical properties of a semiconductor integrated circuit, a liquid crystal display device, and the like formed on a wafer. Usually, this inspection is performed by bringing the probe pins into contact with multiple electrode pads of a semiconductor integrated circuit, a liquid crystal display device, and the like formed on a wafer, which are objects of the inspection.
Such probe pins are required to have not only high electrical conductivity and corrosion resistance, but also properties such as high hardness and high spring characteristics. The reason why high hardness is required of probe pins is that it is necessary to have strength sufficient for withstanding repeated inspection, which is performed millions of times, and the reason why high spring characteristics are requited is that the contact between probe pins and electrode pads is stabilized and that the wear of the probe pins themselves is reduced.
On the other hand, owing to the recent large capacity design of memory devices and miniaturization of packages, the spacing of electrode pads of a semiconductor integrated circuit and the like has become increasingly narrow. Also in a probe card, to cope with the narrow pitch design of electrode pads, it has been required to narrow the pitch of probe pins and to make the wire diameter of probe pins small. To meet these demands, materials for probe pins having sufficient hardness and good workability are sought.
Conventionally used materials for probe pins are those containing tungsten (W) as described in Japanese Patent Application Laid-Open No. 10-038922, those using an alloy obtained by adding silver and the like to palladium (Pd) as described in the Japanese Patent Application Laid-Open No. 11-94875. These materials are used appropriately in accordance with the types of electrode pads of a semiconductor integrated circuit and a liquid display device, which are the objects of inspection. Aluminum pads and gold pads are mainly used as these electrode pads. In probe pins for aluminum pads, tungsten which is a high hardness metal is used so as to be able to break oxide films formed on the pad surfaces. In probe pins for gold pads, it is a general practice to use palladium alloys which have generally high hardness although they have lower hardness than tungsten, in order to prevent the pad surfaces from being damaged.
However, when tungsten is used in probe pins, the following problem arose because of the oxidation easiness of tungsten. That is, when probe pins come into contact with the electrode pads of an object of measurement, tungsten oxide films on the probe pin surfaces exfoliate and adhere to the electrode pads. Therefore, if a continuity test is carried out in this state, poor conduction occurs and accurate measured values cannot be obtained.
On the other hand, when palladium alloys are used in probe pins, sufficient hardness for probe pins is not obtained by usual wire drawing although palladium alloys have electrical conductivity and oxidation resistance necessary for probe pins. Therefore, materials must be fabricated by performing precipitation hardness in order to obtain sufficient hardness, posing a problem that the number of manufacturing steps increases.
The present invention has been made in view of the above circumstances and provides a material which has sufficient hardness for probe pins and is excellent in oxidation resistance and workability in addition to electrical conductivity and high spring characteristics.